Kathleen White of Raynham suffered a traumatic brain injury during an Army National Guard tour of Iraq in 2004. In her first year back home, she would not leave the house. In her second year, she ventured outside to the mailbox. But in her third year, she began to live again.

On Saturday morning, White will continue that journey as she cycles around historic Concord with 50 disabled veterans and about 400 other riders in a display of how camaraderie, competition, and compassion can salve both body and soul.

“When you’re in a bike, you’re free, you’re outside, and it’s liberating,” said White, 39, who will use a three-wheel bike that allows her to sit back and pedal. “I never thought I’d be in the place I am now.”

She credits the psychological and physical benefits of the Wounded Warrior Project, a national nonprofit group that is sponsoring the cycling event, called Soldier Ride. For White, it is a chance to mingle with veterans from around the country who not only share the language of war, but who also understand where their disabilities have taken them and where these veterans want to go.

Some of the veterans are amputees, some have post-traumatic stress disorder, and others, like White, suffer from the long-term effects of serious brain injuries.

John Tlumacki/Globe Staff

Chris Loiselle and other veterans prepared for the event by biking on Cape Cod Thursday and Friday.

“We’ll never be who we were, and that’s the scary thing,” White said. “You have to invent your whole life from scratch. I’m trying to find my way now.”

On Saturday, she will be finding her way around the Concord area, beginning about 9 a.m. when the veterans start from the Old Manse, near the Old North Bridge where the “shot heard ’round the world” helped launch the Revolutionary War on April 19, 1775.

‘It’s just great camaraderie that I’ve been missing. I’ve found my brothers, I’ll say it like that.’

The veterans will have a police escort as they leave on a 22-mile loop. They will ride as a group, with the slowest in front, in a show of solidarity. The hundreds of civilian cyclists, who raised money to join the ride, can follow them or choose distances of 100 kilometers (62 miles) or 100 miles.

“I’ll do the shortest one,” former New England Patriots linebacker Steve Nelson said with a laugh.

Nelson, who starred for the Patriots from 1974 to 1987, will be joined by teammates Steve Grogan and Steve King. For these former professional athletes, the ride is a chance to celebrate the hard-won athletic achievements of others.

“The sacrifice these men and women made for our country, made for our freedom, should never be taken for granted,” Nelson said.

“One of the real dangers is to forget, but you know how life is,” Nelson said. “Everything is on a cycle — what’s the new issue or whatever — but this is something that we can never push to the back burner. We’ve got to take care of our people.”

Organizers are expecting to raise about $100,000, which will help the Wounded Warrior Project continue its mission to enable disabled veterans to enjoy active and healthy lives.

Aimee Falchuk, a Boston resident, is both organizer and rider.

“It’s quite a sight,” Falchuk said of the event, now in its fourth year. “You look for opportunities to support veterans, and often those are in a financial way. But when there’s an actual way to participate in someone’s recovery, it’s such an amazing experience.”

For Chris Loiselle, an Air Force special operations veteran from Chelmsford, the ride is a milestone in his long struggle with post-traumatic stress. He and the other veterans prepared for the ride by biking on Cape Cod for a total of nearly 50 miles Thursday and Friday.

They bused back to Boston with a State Police escort, were scheduled to attend the Red Sox game Friday night, and planned to take a duck boat tour after the ride Saturday.

“This whole trip is just a bunch of people who are going through, and have been through, what I’m dealing with,” said Loiselle, who served two tours in Iraq and one in Afghanistan. “It’s just great camaraderie that I’ve been missing. I’ve found my brothers; I’ll say it like that.”

Over the last several years, the 35-year-old had found that even routine activities such as shopping or going to the movies were a struggle. Anxiety attacks and depression haunted him.

For much of that time, medication helped. But beginning this year, Loiselle gravitated toward exercise and healthy eating as therapy.

“This is huge,” Loiselle said of the fellowship he has enjoyed with other veterans. “You have that every day when you’re active and you’re in the service. But when I got out, it just stopped, and that alone is hard on you mentally and emotionally.”

White, like Loiselle, sees a new world opening up. She knows her life will never be the same, but she has found direction in activities sponsored by groups such as the Wounded Warrior Project and the sports program at the veterans medical center in Brockton.

“We have no normal,” White said. “I don’t know where I fit yet, but I think I fit here for now. I wasn’t in society at all. I didn’t do anything. Now, I owe my life to them.”